NLopt return flag: is there a simple way to check for success?

mcreel · July 22, 2022, 3:41pm

NLopt.optimize returns a tuple (objvalue, xopt, flag), and flag is a symbol that can hold strings such as FTOL_REACHED or SUCCESS. The C API mentions that positive return values indicate success. Is there a similar way to test for success or failure with the Julia package? I can’t figure out how to get beyond a string, which I obtain using println("$flag"). I don’t see how to find an associated numerical value.

odow · July 22, 2022, 9:59pm

You can see the return codes here:

github.com

JuliaOpt/NLopt.jl/blob/c93b84844e7e372d03658a90b7f1cf108969bc2a/src/NLopt.jl#L66-L78


      
          @enum Result::Cint begin
              FORCED_STOP=-5
              ROUNDOFF_LIMITED=-4
              OUT_OF_MEMORY=-3
              INVALID_ARGS=-2
              FAILURE=-1
              SUCCESS=1
              STOPVAL_REACHED=2
              FTOL_REACHED=3
              XTOL_REACHED=4
              MAXEVAL_REACHED=5
              MAXTIME_REACHED=6
          end

but unfortunately NLopt returns a Symbol instead of the enum:

github.com

JuliaOpt/NLopt.jl/blob/c93b84844e7e372d03658a90b7f1cf108969bc2a/src/NLopt.jl#L622


      
          
          
function optimize!(o::Opt, x::Vector{Cdouble})
              if length(x) != ndims(o)
                  throw(BoundsError())
              end
              opt_f = Array{Cdouble}(undef,1)
              ret = ccall((:nlopt_optimize,libnlopt), Result, (_Opt, Ptr{Cdouble},
                                                               Ptr{Cdouble}),
                          o, x, opt_f)
              ret == INVALID_ARGS && chk(o, ret)
              return (opt_f[1], x, Symbol(ret))
          end
          
          
optimize(o::Opt, x::AbstractVector{<:Real}) =
            optimize!(o, copyto!(Array{Cdouble}(undef,length(x)), x))
          
          
############################################################################
          
          
include("MPB_wrapper.jl")
          include("MOI_wrapper.jl")

So you probably just need to deal with each of the possible return values.

Or something like

is_success(ret::Symbol) = ret == :SUCCESS || endswith("$ret", "_REACHED")

mcreel · July 23, 2022, 4:35am

Thanks, I will use this option.